Chronic degenerative radiculomyelopathy (CDRM) is the name proposed for the chronic ataxic syndrome of older dogs previously reported as chronic ossifying pachymeningitis. The condition occurs in dogs of 6 years and older and affects large breeds. There is a slowly progressive ataxia and weakness of the hind limbs. Clinical testing demonstrates abnormalities in proprioception and touch and the nails of the affected leg(s) are usually worn. In the present series 70 % of cases had depression or absence of the patellar reflexes. Pain sensation, bladder control and the panniculus reflex are normal. There are degenerative lesions in the lumbar dorsal columns, fasciculus gracilis, lateral cortico spinal tract and around the ventro-median fissure. In many cases the dorsal nerve roots are also involved. The thoraco-lumbar grey matter and nucleus gracilis show marked astrocytic sclerosis. The distribution of the lesions suggests that this is a ‘dying back’ disease confined to the central nervous system.